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In 1943, N. P. Brantly began the design of a lightweight helicopter, built and flown in 1946 under the designation Brantly B-1. The B-1 was constructed by his employer, the Pennsylvania Elastic Company. Brantly used a coaxial twin-rotor configuration but the design was too heavy and complicated to appeal.

With two co-axial contra-rotating three-bladed rotors, neither push rods nor cranks were visible in the rotary wing assembly. The collective, cyclic and differential controls were completely enclosed in the hubs and ran in an oil-bath.

The three-blade rotors had a fixed pitch central "star" and a universal joint combining two hinges was 1.8 metres from the root of the blades. The radius of the non-flapping part of the blades was 1.8 metres. Each blade weighed only 5.5 kilos and the rotors normally turned at 320 r.p.m.

The B-1 prototype (NX69125) was powered by a 150hp Franklin engine in the tube and fabric fuselage and had a fixed tailwheel undercarriage and directional control was achieved through a small rudder on the sternpost - because the twin main rotors were expected to neutralise the normal torque effect.